Transactions

Group multiple operations into atomic units.

Basic Syntax

:BEGIN
:COMMIT
:ROLLBACK

Simple Transaction

:BEGIN

:UPDATE Account SET balance = balance - 100 WHERE id = 1
:UPDATE Account SET balance = balance + 100 WHERE id = 2

:COMMIT

Database	Output
PostgreSQL	`BEGIN; UPDATE accounts SET balance = balance - 100 WHERE id = 1; UPDATE accounts SET balance = balance + 100 WHERE id = 2; COMMIT;`
MySQL	`START TRANSACTION; UPDATE accounts SET balance = balance - 100 WHERE id = 1; UPDATE accounts SET balance = balance + 100 WHERE id = 2; COMMIT;`

Rollback

Undo all changes in the transaction.

:BEGIN

:UPDATE Account SET balance = balance - 100 WHERE id = 1
:UPDATE Account SET balance = balance + 100 WHERE id = 2

:ROLLBACK

Savepoints

Create checkpoints within a transaction.

:BEGIN

:INSERT Order WITH user_id = 1, total = 99.99
:SAVEPOINT order_created

:INSERT OrderItem WITH order_id = 1, product_id = 5, quantity = 2
:INSERT OrderItem WITH order_id = 1, product_id = 8, quantity = 1

:COMMIT

Database	Output
PostgreSQL	`BEGIN; INSERT INTO orders ...; SAVEPOINT order_created; INSERT INTO order_items ...; COMMIT;`

Rollback to Savepoint

Undo changes back to a savepoint.

:ROLLBACK TO order_created

Release Savepoint

Remove a savepoint (keep the changes).

:RELEASE SAVEPOINT order_created

Isolation Levels

Control how transactions see each other’s changes. Set isolation level before BEGIN.

:SET TRANSACTION ISOLATION LEVEL SERIALIZABLE
:BEGIN

:GET Product WHERE id = 1
:UPDATE Product SET quantity = quantity - 1 WHERE id = 1

:COMMIT

Level	Description
`READ UNCOMMITTED`	Can see uncommitted changes from other transactions
`READ COMMITTED`	Only sees committed changes (PostgreSQL default)
`REPEATABLE READ`	Consistent reads within transaction (MySQL default)
`SERIALIZABLE`	Full isolation, transactions appear sequential

Database	Output
PostgreSQL	`SET TRANSACTION ISOLATION LEVEL SERIALIZABLE; BEGIN; ...`
MySQL	`SET TRANSACTION ISOLATION LEVEL SERIALIZABLE; START TRANSACTION; ...`

Complete Examples

Money Transfer

:BEGIN

:UPDATE Account SET balance = balance - 500 WHERE id = 1 AND balance >= 500
:UPDATE Account SET balance = balance + 500 WHERE id = 2

:INSERT TransactionLog WITH from_account = 1, to_account = 2, amount = 500

:COMMIT

Order with Savepoint

:BEGIN

:INSERT Order WITH user_id = 42, status = "pending", total = 0
:SAVEPOINT order_created

:INSERT OrderItem WITH order_id = 1, product_id = 5, quantity = 2, price = 29.99
:INSERT OrderItem WITH order_id = 1, product_id = 8, quantity = 1, price = 49.99

:UPDATE Order SET total = 109.97 WHERE id = 1
:UPDATE Product SET quantity = quantity - 2 WHERE id = 5
:UPDATE Product SET quantity = quantity - 1 WHERE id = 8

:COMMIT

High Isolation Transaction

:SET TRANSACTION ISOLATION LEVEL SERIALIZABLE
:BEGIN

:GET Account WHERE id = 1
:UPDATE Account SET balance = balance - 100 WHERE id = 1

:COMMIT

Database Support

Feature	PostgreSQL	MySQL	MongoDB
BEGIN/COMMIT/ROLLBACK	Yes	Yes	Yes (sessions)
SAVEPOINT	Yes	Yes	No
ROLLBACK TO	Yes	Yes	No
RELEASE SAVEPOINT	Yes	Yes	No
Isolation Levels	Yes	Yes	Yes (read concern)

MongoDB Note

MongoDB supports multi-document transactions in replica sets and sharded clusters (v4.0+). Savepoints are not supported.

// MongoDB equivalent
session.startTransaction();
db.accounts.updateOne({ _id: 1 }, { $inc: { balance: -100 } });
db.accounts.updateOne({ _id: 2 }, { $inc: { balance: 100 } });
session.commitTransaction();

Limitations

Not currently supported:

BEGIN READ ONLY
Inline isolation level (BEGIN ISOLATION LEVEL X)
Nested transactions

Next Steps

Permissions

Control access

PostgreSQL

PostgreSQL specifics

Getting Started

Queries

Mutations

Schema

Control

Reference

Databases

Integration

Basic Syntax

Simple Transaction

Rollback

Savepoints

Rollback to Savepoint

Release Savepoint

Isolation Levels

Complete Examples

Money Transfer

Order with Savepoint

High Isolation Transaction

Database Support

MongoDB Note

Limitations

Next Steps

Permissions

PostgreSQL

​Basic Syntax

​Simple Transaction

​Rollback

​Savepoints

​Rollback to Savepoint

​Release Savepoint

​Isolation Levels

​Complete Examples

​Money Transfer

​Order with Savepoint

​High Isolation Transaction

​Database Support

​MongoDB Note

​Limitations

​Next Steps

Permissions

PostgreSQL

Basic Syntax

Simple Transaction

Rollback

Savepoints

Rollback to Savepoint

Release Savepoint

Isolation Levels

Complete Examples

Money Transfer

Order with Savepoint

High Isolation Transaction

Database Support

MongoDB Note

Limitations

Next Steps